Telescope Fleet Maintenance

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What does the astro Prof do over the summer? Clean up all the equipment his students have gummed up over the course of the school year! All the scopes rotate through my garage for cleaning and regular maintenance every summer, and I thought some of you might like to see what I do with them.

Teens and Twenty-somethings aren't particularly known for their tender loving care of equipment - especially when it isn't theirs. Our school telescopes see roughly 40 nights of service each school year, with an average of 50 or more students per event. The scopes are carried from the classroom to the football pitch, about 500 m away, set up, then taken down and packed back down to the classroom. This amounts to a lot of hands on time, not to mention a lot of exposure to dust and vibration. Each summer, I take each unit completely apart, clean optics and mount, lube the mount, balance and collimate the scope. It is a fair bit of work, but the scopes that are 12 years old are virtually indistinguishable from the new models; so I must be doing something right!

Today's work was two 150mm f/5 dobs, marketed here by Orion USA as the "Star Blast 6". They are lovely wide-field instruments that are terrific for teaching students how to manipulate a dobsonian telescope.

The photos here show the two scopes in the living room on the coffee table (thank you, Mrs. Astra! ). The OTA is removed from the mount. You can see the dirt and smudges all over the scope! (Thanks, kids!!! ) The area underneath the teflon altitude bearing pad is particularly icky!

I put a piece of tape on the mirror cell to show which screw hole lined up with the logo on the tube for easier reassembly! Once the cell was removed (4 screws), the mirror is easily released from the cell by removing the mirror clamps (6 screws). You can see how dirty the mirror is here!, and the before/after shot. It isn't perfect (this is also one of the older scopes...), but it is vastly improved. I use a wet cleaning process and blow off the water droplets after the surface is clean. I don't ever wipe the optical surface!

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With the primary mirror out, the secondary is given a similar quick clean. Before the optics are replaced, the OTA is cleaned and given a coat of high quality car wax. This has helped preserve the paint finish and they clean up more easily when they've been waxed!

Once the tubes are cleaned and polished, the optics are reinstalled and recollimated using a Lasermate Deluxe from Orion USA <Link>. I like it very much, because I can adjust the scope and see how well collimated I am as I work. So much easier than my old laser collimator! I don't have any business relationship with Orion by the way, except that of satisfied customer. The scope and mount are reunited, and balanced. Before reassembly, the bearing surfaces that the teflon pads ride on are also given a coat of car wax. The ball bearings in the altitude axis are also relubed, I use pool and spa lube because it is a bit thinner than lithium grease, less messy and does an even better job of preventing corrosion. Great stuff. The reassembled scopes move very smoothly without any stickyness that can make a light weight dob frustrating to use.

The garage photo is two of the 150mm f/8's and the two 150mm f/5's all grouped around the tripod for my big refractor just for scale... and for fun! I usually rotate the scopes through here, but this year, I may try to get them all here at one time and take a 'group photo' with all the reflectors out in the back garden!

Awesome! I'll have a Reflectorgarten!

Dan

[tbird]

Interesting to read how well your telescopes are standing up to the use.

I like to use car wax to keep the paint on the OTA clean as well.

Do you have to give the focuser any attention ?

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Old-fashioned rack and pinon focusers get new silicon grease lube about every other year. Mineral spirits on an old toothbrush gets rid of old grease pretty quickly, then relube (VERY thin coat) and away you go. Some focusers have a stick-on felt pad inside that serves as a friction bearing for the focus tube to slide on. I replace these if the old one seems worn out - maybe about every 4-5 years. Newer crayford focusers need virtually no maintenance, ditto with most of the modern two-speed focusers.

Dan